.box{
    background: url(
    https://xwt-leyou.oss-cn-shanghai.aliyuncs.com/1.jpg) center/cover no-repeat;
    width:500px;
    margin: 0 auto;
    background-color: bisque;
    height: 700px;
    margin-top: 20px;
    position: relative;
    display: block;
    margin-bottom: 20px;
}
.form{
    margin-right: 20px;
    opacity: 0.8;
    text-align: center;
}
.head{
    text-align: center;
}

body:before {
    background: url(https://xwt-leyou.oss-cn-shanghai.aliyuncs.com/3307c0db9974786f8fb4c1d4bcb495aebb0c84d8385b7-dziSHf_fw658.jpg) center/cover no-repeat;
    content: '';
    background-repeat: no-repeat;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: -1;
    opacity: 0.8;
    -webkit-filter: grayscale(40%);
    -moz-filter: grayscale(40%);
    /*-ms-filter: gray(40%);*/
    -o-filter: grayscale(40%);
    filter: grayscale(40%);
    /*filter: gray;*/
}
.cover:after {
    position: absolute;
    content: '';
    width: 100%;
    height: 100%;
    top: 0;
    left: 0;
    box-shadow:0 0 50px 30px #ffffff inset;
}

